SINGAPORE (Reuters) - Singapore Prime Minister Lee Hsien Loong said on Saturday a mounting trade spat between the United States and China was one of the most pressing worries for Southeast Asian nations as their leaders echoed the concern over rising protectionism.

Lee flagged his concerns in remarks made as he opened a summit of the 10-member Association of Southeast Asian Nations (ASEAN), for many of which the United States and China are the top two trading partners.

“In particular, the recent trade tensions between the U.S. and China are worrying concerns,” he said. Singapore occupies the group’s rotating chair for this year.

“We are deeply concerned over the rising tide of protectionism and anti-globalisation sentiments,” said a statement issued on behalf of the ASEAN chair at the end of summit talks.

The U.S. Trump administration has threatened to impose tariffs on up to $150 billion of Chinese imports, and Beijing has vowed retaliation against American exports.

On Saturday Lee said the open and rules-based multilateral trading system, which has backed the growth of ASEAN, has come under pressure as the political mood in many countries has shifted against free trade.

There was little progress on the push to resolve the humanitarian crisis in Myanmar, despite a fresh plea by ASEAN leaders for Myanmar to implement the recommendations of an international panel.

The situation in Myanmar’s western state of Rakhine, where hundreds of thousands of minority Rohingya Muslims have fled for neighbouring Bangladesh after a military crackdown, is one of the biggest challenges facing the ASEAN group.

Lee said negotiations for a code of conduct in the South China Sea had started last month between ASEAN and China, and there was hope for an early conclusion. Four ASEAN member states have claims to the disputed South China Sea, one of the world’s most volatile hotspots and one of its busiest waterways.

“We emphasised the importance of non-militarisation and self-restraint in the conduct of all activities by claimants and all other states...that could further complicate the situation and escalate tensions in the South China Sea,” the chair’s statement said.

ASEAN, formed more than half a century ago, has struggled with challenges facing the region because it works by consensus and is reluctant to get involved in matters considered internal to its members.

Singapore is this year’s chair of the bloc, which includes Myanmar, Laos, Cambodia, the Philippines, Thailand, Indonesia, Malaysia, Brunei and Vietnam.

The group is working on initiatives to jointly tackle the threat of extremism and cyber attacks, as well as to promote trade and cross-border e-payment systems.

Meanwhile ASEAN welcomed Friday’s summit meeting of the two Koreas and their pledge to work for peace and a nuclear-free Korean peninsula, as well as the plans for U.S. President Donald Trump to meet North Korean leader Kim Jong Un.